Aeroplane propeller



1931. R. w. scHRoEDER-t' ,351

AEROPLANE PROPELLER Filed Aug. 2, 1930 4 Sheets-Sheet 1v J a l wl w W Dec. 1, 1931. R. w. SCHROEDER AEROPLANE PROPELLER Filed Aug. 2. 1950 4 Sheets-Sheet 2 Dec. 93 R. .,.sn6E DER 1,834,351

Q I WAEROPLANE PROPELLER Filed Aug. 2, 1930 4 Sheets-Sheet 4 Patented Dec, 1931.

nunom'n w. scrmorznnn,

or ennnvinw, ILLimoIs .AEBJOPLANE PROPELLER Application filed August 2,

This invention relates to aeroplane propellers in which the pitch of theblades may be varied to suit various requirements.

When an aeroplane is atrest and it is desired to take-ofi with that aeroplane, it requires a considerable amount-of power to get the aeroplane into motionand into the air. Therefore, when the aeroplane is rising on the take-ofi' a low pitch for the propeller blades is desirable. Thislowpitch is also very desirable for climbing after the machine is in the air, but for rapid flight in a substantially horizontal direction, or in a downward direction, a high pitch is found to be desirable.

One object of my invention therefore is to provide a propeller having blades which are 7 angularly adjustable about an axis at substantially rightangles to the axis of rotation .20 .ofthepropeller, since it is very desirable to,

have aeroplane propeller which is so con structed that the blades thereof may be moved -so as to give either a high or a low pitch thereto. 7

. 'M'ore specifically my invention contemplates the provision of means for varying the angular positions ofethe blades by a simple operation controlled by the pilot of the aeroplane. The pilot merely has to slow down speed and then increase the speed of the propeller thereafter to change the blades from one pitch to another.

In order to accomplish the rotation of the blades of thepropeller about an axis perpendicular to the aids of rotation of the propeller, I prefer to employ a propeller so constructed as to be rotated by means of the centrifugal force acting on the mass of the blades as the propeller rotates:

A still further object of'this invention is Y to provide a propeller which is very simple in design, and is more rugged than any .of the devices nowlniown to those skilled inthe art to which this invention pertains;

' In the drawings- Fig. 1 represents aside view of the mecha-' nism for rotating the blades of the propeller in one direction about their longitudinal axes 5 and the stop mechanism for limiting the the blade;

the speed of the propeller to a predetermined 1930. Serial No. 472,615.

movement of the propeller blades'in the opposite direction; Fig. 2 is a detailed'view of a part of the mechanism shown in Fig. 1;

Fig. 3 is a cross-section through the hub structure of the propeller showing the manner in which the propeller blades are ro- 'tatably mounted on the hub;

Fig. 4 is a cross-section on the line 41- 4 of or Fig. 5 shows the equalizing yoke for the propeller blade;

Fig. 6 is a cross-section taken substantially along the line 66 of Fig. 1; p

Figs. 7 and 8 are detailed perspective views as of parts of the mechanism shown in Fig. 6;

Figs. 9; 10 and 16 are diagrammatic views showing the action which the centrifugal force has on the centers. of'inass of the two portions of each propeller bladewhich lie 7 on opposite sides of the center of rotation of Fig. 11 is a diagrammatic view of the propeller as the same would appear as viewed from the front of an aeroplane upon which the propeller is mounted, the stop mechanism being removed Fig. 12 shows the position of one of the propeller blades and the stop mechanism when the propeller is being used for travelso ing at high speeds;

Fig. 13 shows the position of the same propeller blade as shown in Fig. 12 when the propeller is being used for climbing or taking off;

Fig. 14 illustrates the position to which the blade is moved 'when it is desired to change from a low pitch to a high pitch, or from a high pitch to a low pitch;

1 Fig. 15 is an enlarged top view of the 'device shown in Fig. 14 with the blades in a different position of adjustment.

Referring nownnore particularly to Fig.

3, the reference numeral 1 represents the tapered forward end of the propeller shaft 9 of an aeroplane and 2 represents the hub portion of the propeller which is keyed to the propeller shaft by the key 3 in a well known manner. The hub portion 2 has outwardly extending stubshafts 4 formed in- 1 E tegraltherewith. Each of the stub shafts 4 is provided with a bearing portion 5, and

v a race 6 is fitted over this bearing portion.

"A second race 7 is fitted within a sleeve 8 screw threaded into the respectivepropeller blade 9. Antifriction rollers 10 are interposed between the races 6 and 7 so that the propeller blade will rotate freely about the stub shaft in a direction about the longitudinal axis of the stub shaft and propeller blade. Similarly the outer end of each of the stub shafts is provided with a bearing portion 11 about which is fitted a race 12, a second race 13 being fitted within the hearing surface 14 on the interior of the propeller blade. Antifriction rollers 15 are inter.- posed between the races 12 and 13, and assist the antifriction rollers 10 to provide relatively free rotation for the propeller blades about the axis of the stub shaft. 7

Due to the high speed at which the propeller is required to rotate centrifugal force tends to move the propeller blade outwardly in a direction along the longitudinal axis of of a lock nut 18 and a lock washer 19, the

lock nut being screw threaded on a portion of the stub shaft which is slightly smaller in diameter than the portion upon which the thrust bearing is screw threaded. I interpose a suitable antifriction bearing between the thrust bearing 17 and the enlarged end 20 of the sleeve 8. This comprises the races 21 and 22 and antifriction rollers 23, the latter being interposed between the races as is clearly illustrated in Fig. 3.

With the construction just referred to, it will be seen that while the propeller blades are free to rotate about the axes of the stub shafts 4, they are not permitted to have any movement in a direction longitudinally of the said axes.

In the preferred form of my invention I employ spring means for normally holding theblades of the propeller at -a relatively high pitch, and I will now proceed to describe this means and the means for equaliz-- ing the movement of the propeller blades so that one propeller blade will not rotate to a different angle of pitch than the other propeller blade.

Referring more particularly to Figs. 1, 3 and 6, it will be seen that the hub 2 has a screw threaded portion 24 at the forward end thereof and upon this Iscrew the nut 25 which fits within a suitably formed recess in the forward end of the hub 2 as best seen in Fig. 3. This nut 25 has an enlarged head 26 at its inner end and a second nut 27 screw threaded at 28 to the hub portion has the inner end thereof adapted to. engage and bear against the enlarged head of the nut 25, thus preventing the nut 25 from working loose and preventing the propeller from slipping off the propeller shaft 1.

On the forward end of the hub 2, I screw thread a collar 29, this collar having the integrally formed outstanding cars 30 reinforced by ribs 31. A shaft 32 as best seen in Fig. 6 passes through the ears 30 and is provided with nuts 33, which are threaded on opposite ends of the shaft to prevent longitudinal movement thereof, and these nuts are held in place by the cotter pins-34 or equivalent fastening means.

Mounted on the shaft 32 is a drum comprising the outer c lindrical member 35 and the side walls 36. n the exterior surface of each of the side walls 36 I provide brackets 37 and these brackets are connected by means of a stud bolt 37 held in place by means of the nuts 38 screw threaded on each end of the bolt 37. A coiled spring 39 has the coils thereof wrapped about the cylindrical surface 35 of the drum and each end of the coiled spring is provided with an eyelet 40 for a purpose which will appear later. The ends of the coils are arranged between the bolt 37 and the cylindrical surface of the drum 35 and the bolt 37 therefore maintains a predetermined amount of tension in the coiled spring.

On the outer surface of each propeller blade adjacent the hub of the propeller, I provide a split collar 41, and this split collar has lugs 42 and 43 thereon adjacent the split portion of the collar. A bolt 44 provided with a nut 45 is used to hold the ends of the split collar together, and to clamp the split collar tightly in place on the propeller blade. The colhr 43 is provided with an outstanding integral bracket 46 having an opening 47 therein.

In the eyelets 40, in each end of the springv 39, I arrange a bolt 48. This bolt also passes through a swivel 49, and the bolt is held in place by a nut 50. The clevis 49 is free to rotate about the bolt 48. A metal strap or wire 51' 15 connected to the bracket 46 and also to the swivel 49 it being understood that the swivel 49 has an opening therethrough through which the looped portion- 52 of the strap may extend, the other end of the strap passing through the opening 47 in the U- shaped bracket 46. Thus it will be seen that each of the straps 51 will tend to rotate its respectlve propeller blade about the axis of said stub shaft, and this rotation'is in such a direction as to move the propeller blades to a greater pitch.

From the preceding description it will be seen that the spring 39 tends to move the propeller blades in one direction, that directionbeing such a direction as to give to the blade the maximum permitted pitch or at'leasta greater picth. The sprin 39 is not extreme- 1y strong, but is suflicient y so as to move the blades of the propeller in the directions indicated when the propeller is stationary or rotating at a relatively slow speed. In order to move the propeller blades in the opposite direction, I avail myself of the centrifugal force which acts on the centers of mass of the parts of the propeller blades which lie on opposite sides of the centers of rotation thereof.

The propeller blades are provided with leading edges 53 and trailing edges 54. The blades rotate about the axes indicated by the center lines 55. The centers. of mass 56, 56b,

56c, and 56d lie on opposite sides of the cen-' ter lines 55. These centers of mass rotate in planes, such as 59 having a fixed perpene dicular distance Z to axis 57 and perpendicu:

lar to center line 59. I will now describe the action of the centers of mass under the actionof centrifugal force developedduring the rotation. of the propellers.

Figure 9 shows the position ofthe center of mass 56 when the propeller is at rest and from the axis 57 as is possible. The extreme positionavould be in theplane of rotation 58. In the present instance however, I have shown an'intermediate position 56a. X and X indicate the distances between the. center of mass when at 56 and 56a respectively and the plane 58. Y and Y similarly represent the distances to the plane through 57 and 59. W and W indicate the straight line distances to the center of mass when at 56 and 56a respectively. a Y I .It is obvious that the value W is greater than W so that it is readily appreciated that the center of mass will'move from 56 to 56. instead of in the opposite direction, for when moving in the opposite direction W will decrease. The theoretical arm a which carries the center of mass will, therefore, move to position a. Since 0; represents somewhat the actual pitch angle of the blade, it will be seen that the pitch of the blade is decreased as the centrifugal force increases. The position of arm a. does not actually represent the pitch angle of the blade, but the arm a does bear a fixed relation to the pitch angle of the blade.

' In Fig. 16 I have indicated in dotted lines the position of the center of mass 56?) which, as will be seen from Fig. 11, lies on the opposite side of the center line 55. The tendency is .for the center 566 when acted upon by centrifugal force to also move towards the plane of rotation 58 and of course since this movement tends to rotate the blade 9 as a whole in the same direction as the center of mass 56, the two forces unite to rotate the blade and do not oppose each other.

- There are therefore two forces tending to rotate the blades of the propeller when the propeller is rotating. One of these forces is the spring which tends to rotate the propeller blades from a low pitch to a high pitch and the other is the centrifugal force which tends to rotate the propeller blades from a high pitch to a low pitch. When the propeller is rotating at a relatively slow speed, the force of the spring is sufficient to overcomethe centrifugal force at that speed and conse uently the blades are moved to a highpitc If the speed of the propeller, however, is 111-:

creased to amaximum speed,-or the speed which is desired for propelling the aeroplane, the centrifugal force increases to such an extent that it overcomes the action of the spring 39 as well as the friction which occurs in the thrust bearing which comprises the races 21 and 22 and antifriction rollers 23. The

centrifugal force therefore rotates the blades from a high pitch to a low pitch, or at least a lower pitch than the blades normally occupy when the propeller is at rest or moving at a relatively slow speed.

I now wish. to describe the mechanism I whereby I govern the pitch to which the enable one to select any one of' a number of pitches to which the blade may be moved nnder the action of centrifugal force. Preferably however, I provide a stop member having only two surfaces which I shall denote cam surfaces andagainst which a stop carried by the blade is adapted to abut. I also provide mechanism for selecting the particular cam surface against which the stop is to abut. Any unbalancing, which may be occasioned 'by the off-center location of the stop mechanism and selector mechanism, may be rectified by applying weights equivalent to the unbalanced weight of said mechanisms on the opposite sides and at a proper distance from the axis of rotation of the propeller system. g

The hub 2 is flattened on two opposite sides as at 60, and adjacent these flattened portions are flan es 61 which are integral with the hub an form bearings for the rings 62. These rings 62 are substantially of the same thickness as the flanges 61, and the flat faces of the rings 62 are substantially flush with the flat faces on the flanges 61. Each of the rings 62 and flanges 61 have co-operating flat surfaces abutting against each other as at 63 so as to prevent the ring from rotating relatively to the flange 61. The flange 61 blades are moved under the action of een- 'merely performs has a bearing member 64 secured thereto by any suitable fastening means such as the rivet 65, and on this hearing member 64 I provide a pivot 66 adapted to rotatably sup: port the cam member 67, the detent member 68 and the ratchet member 69, these members being fastened rigidly to each other, or formed from a single piece of material if so desired. The bearing member 64 is also secured to the ring 62 by means of apivot 70, which passes through the bearing member 64, and the ring 62. In other words, the ring 62 the function of abearing surface upon which the bearing member 64 may be secured and the device would operate equally as well if the ring 62 were formed as an extension of the flange 61. For the purposes of construction however, it is preferred to have the ring 62 and the flange 61 separate members. v

The pivot 70 also carries a detent member 71 which has a pointed end 72 adapted to be received within the notches 7 3 of the detent member 68. A spring 74 secured to an arm 7 5 of the detent member 71'abuts against the upper surface of the bearing member 64 and 'to 'be received within said notches.

the ring 62, and'tends to rotate the detent member 74 in a counter-clockwise direction as viewed in Fig. 6, the surfaces of the ring 62 and member 64 being substantially flush at this point. Since the pivot 66 and the pivot 7 O are both carried by the member 64 which in .turn is rigid with the hub portion, the detent member 71 will always tend to hold the detent member 68 and consequently" the-cam 67 in any position of adjustment to which the same may be moved by a mechanism which I shall now describe i The split collars 41 each carry aroller 76 mounted on a pivot 77, screw threaded as at 78 '(see Fig. 3) to the split collars 41. A yoke member 79 has an opening 80 therein which is rotatably mounted on a bearing portion 80 of the hub 2 as best illustrated in Figs. 3 and 6. Thisyoke 79 has notches 81 inop posite ends of the flange 82 which forms a part of the yoke and the rollers 76 are adaplttleld e spring 39 tends to rotate the propeller blades in opposite directions, and of course, the centrifugal force also acts to rotate the propeller blades in opposite directions; Regardless of whether it is the spring or the centrifugal force which is acting on the propeller blades to rotate the same, the yoke 79 will tend to equalize the amount of movement imparted to the propeller blades. In other words, one of the propeller blades cannot have a different pitch than the other propeller blade. I do not however, wish to limit myself to this particular means of equalizing the movements of the blades although it will be readily seen that the means which I employ is very simple and yet very eflicient.

I also secure to each of the collars 41 a stop member 81 which is dove-tailed as at 82 (see Fig. 6) to the split collar and held in place "end of the stop member 81, I pivot a pawl 84 at 85. This pawl 84 has a tooth 86 at the end thereof adapted to engage the teeth-87 on the ratchet member 69. A spring 88 is secured to the pawl 84, and is yieldingly urged against the flat surface 60.

I will now proceed to describe the operation of the stop mechanism under the action of the centrifugal force, and also under the action of the spring 39. The collar 41 0 course, is carried by the rotatable blade of the propeller and the ratchet wheel 69, detent member 68 and cam member 67 are all carried rigidly on the hub structure. The pawl 84 is carried by the stop member 81 and of course will move with the stop member 81 and the collar 41. Therefore, in Fig. 6, if the collar 41 is rotated in a clockwise direction, the pawl will be carried therewith in the same direction and this will cause the tooth 86 to engage the adjacent tooth 87, of the ratchet member 79 and rotate the cam member 67 from the position shown in that figure to the position shown in Fig. 13. This brings the low cam surface 89 into a position such that when the collar 41 is rotated in a counter-clockwise direction as viewed in Fig. 6, the stop 81 will abut against this low cam surface instead of the high cam surface 90 as illustrated in Fig. 6, and also in Fig. 13. Similarly when the collar 41 is again rotated in a clockwise direction, the pawl again moves the cam member in a counter-clockwise direction and thus positions the next high cam surface 90 in a position to be engaged by the stop 81 when the collar 41 is again rotated back to the position shown in Fig. 6, or in Fig. 12. In other words, each complete movement of the collar 41 in a clockwise direction and then in a counter clockwise direction brings the next suc- 90. It is possible to have my device operate with only two cam surfaces spaced about the.

periphery of the cam 67, but by providing six cam. surfaces, or three pair of cam surfaces, it is not necessary to rotate the cam through as great an angle for each movement of the collar 41. Or I may provide more cam surfaces, for instance, four pairs of surfaces such as '89 and 90, and I may also provide'in addition -to cam surfaces such as 89 and 90, additional cam surfaces which will permit greater or less movement of toward the cam -member67.

It will be noted that the movement of the the collar 41 in a direction collar 41 in Fig. 6 in a counter-clockwise direction moves the blade 9 also in a counter clockwise direction so as to decrease the an- .gle of pitch which is the angle which the blade makes with the plane of rotation 58. Therefore, when the stop 81 is against the high cam surface 90, the blade 9 is at a greater pitch than when the stop 81 is against the cam surface 89. As stated before, the spring 39 has the tendency to rotate the collar 41 in a direction to move the blades to its maximum permitted pitch and'this would be in a clockwise directionas viewed in Fig. 6. A

A stop 91 on the ring 62 abuts against the stop 81 and limits the amount of rotation which may be given to the blade 9 in a clockwise direction. This position of the blade is illusgal force is the force which tends to rotate the propeller blade to decrease the pitch thereof and this force will act to rotate the collar 41 and sleeve 9 in a counter-clockwise direction" as viewed in Figs. 12, 13 and 14. This centrifugal force overcomes the force of the spring when the propeller is-rotating at-high speeds and therefore when the propeller is rotating at high speeds, the stop 81 is always rotated; against the cam surface which happens to be in operative position, and it Wlll be noted that each successive movement of the stop member81 to the right as viewedin Fig. 6 and then to the left will cause the stop member 81 to engage first the cam surface 90 and then the cam surface 89 and so on.

which has been described is mounted on the propeller shaft of an aeroplane and the plane is on the ground ready to take-off. Before the engine is started the. blades 9 are at a high pitch because of the fact that the same are under the influence of the spring 39. After the motor has been started and the propeller is rotating at a relativelysldw speed,

the propeller blades are still in the position as the centrifugal action moves the propeller blade in a counter-clockwise direction as in Fig. 13, the stop 81' moves closer and closer to the cam surface 89 and finallyengages sald camsurface, arresting any further movement of the-propeller blade in a counter-clockwise direction. The propeller blade being at a low pitch, is suitable'for the pur- 50 3 Let us now assume that the propeller that centrifugal poses of take-ofi as the low pitch gives a very great amount of power in substantially the same manner as the low pitch of a screw thread gives a greater lifting power to a screw jack or other similar mechanical device. After the aeroplane is in the air and it is desired to travel at a high rate of speed,

the pilot slows down the speed of his engine momentarily, and this permitsthe spring 39 to act again as soon as the centrifugal force has been decreased the proper amount.

causes the propeller blade to again move to the position 14, and the pawl 84 will rotate the cam member 67 until the high portion 90 of the cam is inthe position shown in Figs. 6, 12 and 14. The pilot thereafter opens the throttle and increases the speed of the engine causing the centrifugal force to again throw the propeller blade to its minimum permitted pitch which this time is greater than the pitch shown in Fig. 13, for the reason that the cam surface 90 is higher than the cam surface 89,- and therefore arrests the movement of the stop 81 sooner than does the cam surface 89. This pitch of the propeller is preferred for high speeds.

If the pilot should desire to climb to high altitudes while in the air, all that is necessary is to throttle the engine and then again open the throttle. The slowing down of the engine will cause the cam 67 to move to the position shown in Fig. 13 and the speeding up of the engine will thereafter bring the stop 81' against the cam surface 89.

Obviously if one desired another speed or another tractiveeffort for the propeller blade, it would only be necessary to provide be used with a different stop member 87, I hich stop member could be provided wlth cam surfaces at such distances from the center of rotation thereof as would suit theneeds of that particular aeroplane, so that the best possible angles desired for the blades when taking-off and driving at high speed may be given to the propeller when used in any particular machine.

The air pressure may possibly have some action on the blades to tend to-rotate'them another cam surface. .Also for differenttypes of aeroplanes the same propeller could into the plane of rotation but it isbelieved v force and would cause the blades-to operate as described even if the propeller were rotated in a vacuum.

force is by far the greater While I have described the action of centrifugal force on the centers of mass it will be understood that one could consider each individual particle of the mass of the blades separately and the conclusions reached would be the same.

- Obviously a great many changes may be made in the particular construction of the propeller which I have described and shown 1n the accompanying drawings. without departing from the spirit ofthe invention or the scope of the appended claims and therefore I do not wish to limit my invention to the particular details shown in the embodi- .ment disclosed in this application.

Having thus fully described my invention,

.what I desire to secure by Letters Patent of the United States is 1. An aeroplane propeller comprising a ments of said blades under the action of contrifugal force to thereby predetermine the pitch which is to be given to'the propeller blades.

2. An aeroplane propeller comprising a plurality of blades rotatably mounted on a hub portion so as to rotate about axes at substantial angles to the axis of rotation of said hub, said propeller blades being held against bodily movement away from said hub and being rotatable about their own axes by centrifugal force exerted on the mass of the propeller blades in a direction'to decrease the pitch thereof, and an adjustable stop for limiting the movements of said blades under the action of centrifugal force to thereby p're determine the pitch which is to be given to the propeller blades, said stop being controlled by the rotative speed of said propeller to selectively vary the limit of movement of the blades under centrifugal force.

3. An aeroplane propeller comprising a plurality of blades rotatably mounted on a hub portion so as to rotate about axes at substantial angles to the axis of rotation of said hub, said propeller blades being rotatable about their own axes by centrifugal force exerted on the mass of the propeller blades in a direction to decrease the pitch thereof. and stops for limiting the movements of said blades under the action of centrifugal force to thereby predetermine the pitch which is to be given to the propeller blades, said'stops being selectively movable to operable positions and controlled by the speed of rotation of said propeller.

, 4. A11 aeroplane propeller comprising a plurality of blades rotatablymounted on a hub portion sons to rotate about axes at substantial angles to the axis of rotation of said hub, said propeller blades being held against bodily being rotatable about their own axes by centrifugal force exerted on the mass of the movement awayfrom said hub and propeller blades in a direction to decrease the pitch thereof, and stops for limiting the movements of said blades under the action of centrifugal force to thereby predetermine the pitch which is to be given to the propeller blades, said stops being adjustable to selectively' vary the limit of movement of the blades under centrifugal force and selectively rendered operative by varying the speed of rotation of said propeller.

5. In an aeroplane propeller the combination with a rotatable hub member, of a blade member rotatably mounted on .said hub member and held against bodily movement away from said hub member, a stop mounted on one of said members adapted toengage an adjustable stop on the other of said members to limit the rotative movement of said blade member in one direction, the adjustment of said stop being controlled by the speed of rotation of said propeller and a third stop for limiting movement of said blade member in,

the other direction, said blade membegv havr ing means for rotating'the same about its own axis in one direction and being movable in the other direction by the centrifugal force which acts on the mass of said blade member.

6. In an aeroplane propeller the combination with a rotatable hub member, of a blade member rotatably mounted on said hub member and'held against bodily movement away from said hub member, a stop mounted on one of said members adapted to engage an adjustable stop on the other of said members to limit the rotative movement of said blade member in one direction, and a third stop for limiting movement of said blade member in the other direction, said blade member having means for rotating the same about its own axis in one direction and being movable in the other direction by the centrifugal force which acts on the mass of said blade member,

said adjustable stop being for the purpose of varying the angle to which the blade may be moved about its own axis in one direction and being controlled by interconnecting means between said blade'and said adjustable stop,

operable to adjust said stop during move-' ment of the said blade about its axis.

7. In an aeroplane propeller the combination with a rotatable hub member, of a blade rotatably mounted on said hub member. a stop mounted on'said hub member adapted to engage a stop on said blade, one of said stops comprising a member having a plurality of projections thereon which may be selectively positioned to engage the other of said stop members to limit the rotative movement of said blade and determine the angle to which sal 1 blade may be rotated in one direction, said blade being rotatable in a direction to bring said stops in engagement with each other by the centrifugal force acting on the mass of said blade and being rotatable so as to move said stops away from each other by means other than centrifugal force, said last mentioned means acting to move said blade in the last mentioned direction when the centrifugal force has been decreased to a I other by thecentrifugal force acting on the mass of said blade and being rotatable so as to move said stops away from each other by -mcans other than centrifugal force, said last mentioned means acting to move said blade in the last mentioned direction when the centrifugal force has been decreased to a predetermined amount, said stop which has the plurality of projections thereon being selectively movable by the pilot to selectively position the desired one of the projections in a EQSltlOIl to engage the other of said stop memers.

9. A propeller for aeroplanes comprising a hub portion, blades rotatably mounted on said hub portion so as to be capable of movement from a low pitch to a high pitch and from a high pitch to a low pitch, means for moving said blades to a high pitch. means for moving said blades to a low .pitch selectively operable by the pilot of an aeroplane in which said propeller is adapted to be installed, a stop on said hub, a second stop on one of said blades, one of said stops having a plurality of abutments thereon adaptedto engage I the other of said stops to selectively arrest rotative movement of said blades when the stops come into engagement with each other,

and means for selectively moving said stop with the plurality of abutments to position the desired abutment 'in position to engage the other of said stops assaid stops move away from each other.

10. An aeroplane propeller comprising a' hub portion adapted-to be secured to the propeller shaft of an aeroplane engine, rotatable stop members 0 said hub portion, rotatable blades on said ub portion held against bodily movement away from said hub portion and rotatable in' one direction about their own axes by the action of centrifugal force acting on their -masses, a spring for rotating said blades in the opposite direction, a pair of stops on said hub, a stop on each of said blades cooperating'with one of said pair of stops on said-hub-thereby forming two pairs of co-operating stops, each pair comprising a stop on the hub and a stop on the blade. one stop of each of said pair of stbps being adj ustable and having a plurality of abutments thereon adapted to be arranged selectively in a position to engage the other of the stops of each .of said pairiof stops to thereby limit the angular movement of said blade Selectively at the will of the pilot of the aeroplane in which said propeller is installed, said cooperating stops on said blades and hub being movable into engagement witheach other by centrifugal force acting on the masses of said blades and being movable out of engagement with each other by said springs.

11. In an aeroplane propeller comprising a hub, propeller blades rotatably' mounted on said hub, an equalizing member for equalizing the movement of said blades about their axes, means for holdingsaid blades against bodily movement away from said hub, a

fixed stop on each of said blades, a co-operating adjustable stop on said hub for each stop on said blades and for co-operating with the stops on said blades to limit rotative movement of said.blades in one direction, said adjustable stops'having a plurality of' abutment surfaces thereon, each of which is adapted to be positioned selectively to en'- gage the adjacent stop on the adjacent blade,

a spring for moving said blade so that the stops are out of engagement with each other 4 where the propeller is rotating at less than from each othei and means for holding said adjustable stops in desired adjusted position, a

said propeller blades being rotatable against the action of said spring into such a position that the stops on said blades engage their cooperating adjustable stops on said hub by the centrifugal force acting on the mass of said blades after the propeller is rotated at a speed higher than a predetermined amount.

12. A propeller blade as claimed in claim 11 in which the propeller blades are acted upon by a spring so as to be moved to the maximum permitted pitch and in which the hub is provided with a second stop for'limitingthe movement ofs'aid blade under the action of said spring.

13. An aeroplane propeller comprising a.

hub, stub shafts mounted on said hub, propeller blades rotatably mounted by means of suitable antifriction bearings on'said stub shafts, said antifriction bearings comprising 'bearings for assisting rotative movement about said stub shaft and for minimizing the friction caused by centrifugal force in a direction longitudinally of said stub shafts, flanges on said hub adjacent said propeller blades, collars on said propeller blades adja cent said flanges, a stop on each of said coltions,

lars, a pair of stops on each of said flanges adjacent said collars and arranged to abut the stops on the respective collars when the propeller blades are moved in opposite direcone of said stops on each of said flanges comprising a rotatable member having different portions of the periphery thereof at difierent radial distances from the center of rotation thereof, pawl and ratchet mechanism for rotating said last mentioned stop to selectively position the desired portion of the periphery of said last mentioned stop in a position to engage the respective stop on said collars while the stops on said collars and said rotatable stop members are out of engagement with each other, thereby limiting the rotative movement of said blades in one direction a predetermined amount which may be selected upon proper rotation of said rotatable stop member, means for controlling the rotation of said rotatable stop member,

and a spring arranged symmetrically with respect to said hub portion and being operable to rotate both of said blades to a position such that the stops on said collars are out of engagement with said rotatable stops, each of said stops on said flanges other than said rotatable stops being for the purpose of limiting the rotative movement of said blades under the action of said spring, said blades being rotatable in a direction opposite to that in which theyare moved by said spring by the centrifugal force which acts upon the mass of said blades, said stops on said collars and said rotatable stops co-operating to form the limiting means for the rotative movement of said blades under the action of centrifugal forc 14. An' aeroplane propeller comprising a 40 hub, stub shafts mounted on said hub, propeller blades rotatably'mounted by means of suitable antifriction bearings on said stub shaft, said antifriction bearings comprising bearings for assisting rotative movement 15 about said stub shaft and for minimizing the friction caused by centrifugal force in a direction longitudinally of said stub shafts, flanges on said hub adjacent said propeller blades, collars on said propeller blades adj acent said flanges, a stopon each of said collars, a pair of stops on each of said flanges adjacent said collars and arrangedto abut the stop on the respective collars when the propeller blades are moved in opposite directions, one of 'said stops on each of said flanges comprising a rotatable member having different portions of the periphery thereof at different radial distances (from the-center of rotation thereof, pawl and ratchet mechanism 0 for rotating said last mentioned stop to selectively position the desired portion of the periphery of said last mentioned stop in a position to engage the respective stop on said collars while the stops on said collars and 6d said rotatable stop members are out of enmay be selected upon proper rotation of said rotatable stop member, means for controlling the rotation of said rotatable stop member, a spring arranged symmetrically with respect to said hub portion and being operable to rotate both of said blades to a position such that the stops on said collars are out of engagement with said rotatable stops, each of said stops on said flanges other than-said rotatable stopsbeing for the purpose of limiting the rotative movement of said blades under the action of said spring, saidblades being rotatable in a direction opposite to that in which they are moved by said spring by the centrifugal force which acts upon the mass of said blades, said stops on said collars and said rotatable stops co-operating to-form the limiting means for the rotative movement of said blades under the action of centrifugal force, said blades being held against bodily movement away from said hub and equaliz ingmeans for equalizing the rotative movement of said blades about their axes comprising a member rotatable about an axis concentric with said hub and having means interlocking with fixed means on each of said blades. 1

15. An aeroplane propeller comprising a plurality of blades, a hub, spindles extending at substantial angles to said hub upon which said blades are rotatably" mounted, said propeller blades being held against bodily movement away from said hub and being rotatable about their respective spindles by centrifugal force exerted on the mass of the propeller blades in a direction to decrease thepitch thereof, a plurality of stops selectively movable to ope ative positions for limiting the movements of said blades under the action of centrifu a1 force to thereby predetermine the pitch which is to be given to the I propeller blades when said propeller blades are moved against said stops by the action of centrifugal force, and means for selectively moving the stops to operative positions to limit the movement of the blades, said last mentioned means being operable by means on said blades when said blades move to a positated by centrifugal force, and means operable by said blades as they rotate in a direction to move said stops out of engagement with each other for selectively positioning the stops on said hub portion which are to be engaged by the stops on said blades when said blades again move about their respective spindles under the action of centrifugal force. 1

- 1 7. An aeroplane propeller comprising a hub, blades rotatably mounted on said hub, said blades being rotatable about their axes under the action of centrifugal force acting onthe mass of said blades when said blades rotate, a plurality of stops on said hub, a

' 'stop on each of said blades adapted to abut s against a selected one of said sto s on said hub to limit the movement of said lades unv der the action of centrifugal force to thereby determine the angle to which each of the blades moves, and means controlled by the speed of rotation of said hub for selecting the stops on said hub which are adapted to limit the movement of said blades about their reand being rotatable about their own axes by centrifugal force exerted on the masses of propeller blades in a direction to change the pitch thereof and stops movable selectively to operativepositions by the speed of rotation of said propeller for limiting the movements of said blades under the action of centrifugal force to thereby predetermine the pitch to which said blades may move under the action of centrifugal force.

which the movement of the blades about their axes in a direction opposite to the direction in which they move under centrifugal force causes the operation of selecting mechanism 20. A device as claimed in claim 19, in

for selecting the stop, next to be positioned in operative position to limit the movements of said blades under the action of centrifugal force when said blades next move under the action of centrifugal force. v p In testimony whereof I have signed my name to this specification on this 20th day of July, A. D. 1930. v

- RUDOLPH W. SCHROEDER.

spective axes, different stops on said hub being adapted to limit the rotative movement of said blades at different positions "in their paths of rotation.

18. A propeller comprlsing a hub, an adjustable stop on said hub, a blade rotatably mounted on said hub, a cooperating stop on 'said blade, means for moving said last mentioned stop away from said adjustable stop when said hub is rotating at a relatively slow speed and when said hub is not rotating, said blade being rotatableto bring the stop there on into engagement with the cooperating stop on said hub when said hub rotates at relatively high speeds due to the centrifugal force actin on-the mass of said blades, and means opera 1e when, said sto on said blade moves away from saidadjusta 1e stop for adjusting said stop so that when said blade afgain moves under the action of centrifugal orce to bring said stops into engagement'with each other, said blade will have a difieren't limitingposition than on the previous movement of said blade under the action of centrifugal force,

19; An aeroplane propeller comprising a plurality of blades rotatably mounted on a I hub portion to rotate about axes at substantial angles .to the axis of rotation of said hub portion, said'pro'peller blades held against bodily movement away from said hub portion 

